Abstract: Increased efficiency in a multiple agent system is provided by allowing all explicit writebacks to continue during a snoop phase. Upon each incoming external bus request, an agent determines if the address of that request matches an address of data within the agent. If there is a match, the agent copies this most recent data, changes the state of the data to unmodified, changes the length of the data to zero (for pending explicit writebacks), and performs an implicit writeback. Additionally, prior to each explicit writeback, an agent determines if the address of the explicit writeback and any incoming snoop request requests are the same. If there is a match, the agent changes the data length of the explicit writeback to zero prior to issuing the explicit writeback.

Abstract: A scheduler stores data to be scheduled. The scheduler may include an array that identifies relative priorities among the queue entries according to a first priority scheme, such as by age. The scheduler also may include a priority register array identifying relative priorities among the queue entries according to a second priority scheme, such as by data type. A plurality of detectors coupled to the array and to the priority register array may determine which data is to be scheduled next.

Abstract: In a method of processing a bus transaction, an address is retrieved from the bus transaction and referred to a queue of pending transaction. A match indicator signal is returned from the queue. If the match indicator signal indicates a match, a snoop probe for the bus transaction is blocked.

Abstract: A scheduler stores data to be scheduled. The scheduler may include an array that identifies relative priorities among the queue entries according to a first priority scheme, such as by age. The scheduler also may include a priority register array identifying relative priorities among the queue entries according to a second priority scheme, such as by data type. A plurality of detectors coupled to the array and to the priority register array may determine which data is to be scheduled next.

Abstract: Increased efficiency in a multiple agent system is provided by allowing all explicit writebacks to continue during a snoop phase. Upon each incoming external bus request, an agent determines if the address of that request matches an address of data within the agent. If there is a match, the agent copies this most recent data, changes the state of the data to unmodified, changes the length of the data to zero (for pending explicit writebacks), and performs an implicit writeback. Additionally, prior to each explicit writeback, an agent determines if the address of the explicit writeback and any incoming snoop request requests are the same. If there is a match, the agent changes the data length of the explicit writeback to zero prior to issuing the explicit writeback.

Abstract: In a method of processing a bus transaction, an address is retrieved from the bus transaction and referred to a queue of pending transaction. A match indicator signal is returned from the queue. If the match indicator signal indicates a match, a snoop probe for the bus transaction is blocked.

Abstract: Increased efficiency in a multiple agent system is provided by allowing all explicit writebacks to continue during a snoop phase. Upon each incoming external bus request, an agent determines if the address of that request matches an address of data within the agent. If there is a match, the agent copies this most recent data, changes the state of the data to unmodified, changes the length of the data to zero (for pending explicit writebacks), and performs an implicit writeback. Additionally, prior to each explicit writeback, an agent determines if the address of the explicit writeback and any incoming snoop request requests are the same. If there is a match, the agent changes the data length of the explicit writeback to zero prior to issuing the explicit writeback.

Abstract: An error correction system in an agent provides an error correction in a circuit path extending from an internal cache to an output of the agent. When data errors are detected for data to be processed internally within the agent, the error correction system passes the corrupted data through the error correction circuit, and out of the agent and back into the agent. The error correction changes internal data requests into an external transaction when data errors are detected.

Abstract: A method of processing a data request in a processing agent. The method comprises posting the data request internally within the agent and, if the data request implicates data associated with a pending external transaction, canceling and recycling the data request.

Abstract: A method and apparatus for avoiding tag compares when writing to a cache. In a cache hierarchy, location information of the cache entries are linked and supplied to the other caches, during caching of the data from memory. When the processor is ready to update the content of the memory location, the location information loaded into a write buffer allows the write buffer to update the cache(s), without the need for tag comparisons to determine if particular entries are present. The avoidance of the tag compare operation during cache update saves a clock cycle, so that overall processor performance is improved.

Abstract: An error correction system in an agent provides an error correction in a circuit path extending from an internal cache to an output of the agent. When data errors are detected for data to be processed internally within the agent, the error correction system passes the corrupted data through the error correction circuit, and out of the agent and back into the agent. The error correction changes internal data requests into an external transaction when data errors are detected.

Abstract: An error correction system in an agent provides an error correction in a circuit path extending from an internal cache to an output of the agent. When data errors are detected for data to be processed internally within the agent, the error correction system passes the corrupted data through the error correction circuit, and out of the agent and back into the agent. The error correction changes internal data requests into an external transaction when data errors are detected.

Abstract: A prefetching control system provided for a processor. The prefetching queue may include an arbiter, a cache queue and a prefetch queue. The arbiter issues requests including read requests. Responsive to a read request, the cache queue issues a control signal. The prefetch queue receives the control signal and an address associated with the read request. When the received address is a member of a pattern of read requests from sequential memory locations, the prefetch queue issues a prefetch request to the arbiter.

Abstract: A data control method in a microprocessor is disclosed. According to the method, a request is generated on an external bus for data to be read to the processor. The requested data is read from the external bus to an intermediate memory in the processor and, thereafter, read from the intermediate memory to a destination. When the intermediate memory is full, the read of data from the external bus is stalled until the intermediate memory is no longer full. Typically, stalling is accomplished by generating a stall signal on the external bus, which may be generated during a cache coherency phase of the transaction to which the requested data relates.

Abstract: A livelock preventative measure is provided for agents in a multi-processor computing system. Livelock may occur when multiple agents each trade ownership of data in an attempt to modify it. When livelock occurs, a first agent posts a bus transaction for a data and, if a second agent posts a bus transaction for the same data, the first agent may stall the bus transaction of the second agent until the first agent has completed its operation on the data.